Minimizing misdecodes in electro-optical readers

ABSTRACT

An arrangement for, and a method of, minimizing misdecodes of GS1 DataBar Limited (Databar-limited) symbols in a reader for electro-optically reading symbols of different symbologies, such as Universal Product Code (UPC) Version A (UPC-A) symbols, includes a data capture assembly for capturing light from a target symbol, and for generating an electrical signal indicative of the captured light; and a controller for processing and decoding the electrical signal, and for determining whether the decoded signal is indicative of a Databar-limited symbol, and for determining whether the decoded signal has characteristics indicative of a different symbology, such as the UPC-A symbol, to indicate whether a misdecode of the Databar-limited symbol has occurred.

DESCRIPTION OF THE RELATED ART

Moving laser beam readers or laser scanners, as well as solid-stateimaging systems or imaging readers, have both been used, in bothhandheld and hands-free modes of operation, to electro-optically readbar code symbols having different bar and space patterns that are usedto represent different characters. Sets of these patterns are groupedtogether to form a symbology. There are many types of bar codesymbologies, each having their own special characteristics and features.Most symbologies are designed to meet the needs of a specificapplication or industry.

The moving laser beam reader generally includes a laser for emitting alaser beam, a focusing lens assembly for focusing the laser beam to forma beam spot having a certain size at a focal plane in a range of workingdistances, a scan component for repetitively scanning the beam spotacross a target symbol in a scan pattern, for example, a scan line or aseries of scan lines, across the target symbol multiple times persecond, e.g., forty times per second, a photodetector for detectinglight reflected and/or scattered from the symbol and for converting thedetected light into an analog electrical signal, and signal processingcircuitry including a digitizer for digitizing the analog signal, and amicroprocessor for decoding the digitized signal based upon a specificsymbology used for the symbol.

The imaging reader includes a solid-state imager or sensor having anarray of cells or photosensors, which correspond to image elements orpixels in a field of view of the imager, an illuminating light assemblyfor illuminating the field of view with illumination light from anillumination light source, e.g., a laser or one or more light emittingdiodes (LEDs), and an imaging lens assembly for capturing return ambientand/or illumination light scattered and/or reflected from the symbolbeing imaged over a virtual scan pattern, e.g., a virtual scan line or aseries of virtual scan lines, over a range of working distances. Such animager may include a one- or two-dimensional charge coupled device (CCD)or a complementary metal oxide semiconductor (CMOS) device andassociated circuits for producing electronic analog signalscorresponding to a one- or two-dimensional array of pixel informationover the field of view. Again, signal processing circuitry including adigitizer is used for digitizing the analog signal, and a microprocessoris used for decoding the digitized signal based upon a specificsymbology used for the symbol.

It is therefore known to use the imager for capturing a monochrome imageof the symbol as, for example, disclosed in U.S. Pat. No. 5,703,349. Itis also known to use the imager with multiple buried channels forcapturing a full color image of the symbol as, for example, disclosed inU.S. Pat. No. 4,613,895. It is common to provide a two-dimensional CCDwith a 640×480 resolution commonly found in VGA monitors, although otherresolution sizes are possible.

As advantageous as both types of readers are in reading symbols, it isdesirable in many applications for each reader to read symbols ofdifferent symbologies. One older, omnipresent symbology is the UniversalProduct Code (UPC) Version A (UPC-A) symbol, which is comprised of alinear arrangement of bars and spaces (each termed as an element) ofvarious widths that, when decoded, uniquely identify a product and itsmanufacturer. Another newer symbology is the GS1 DataBar Code, which wasformerly known as the Reduced Space Symbology (RSS) code, and especiallythe GS1 DataBar Limited (Databar-limited) code whose symbol is more than50% smaller than the UPC-A symbol and, hence, makes it particularlyuseful for identifying small and hard-to-mark products such as produceand pharmaceutical items. The Databar-limited symbol is also comprisedof a linear arrangement of bars and spaces (each termed as an element)of various widths that, when decoded, uniquely identify a product andits manufacturer, as well as additional information, such as serialnumbers, lot numbers and expiration dates and, thus, provides forgreater product identification, traceability, quality control, and moreflexible coding for coupon applications. The Databar-limited symbol isdesigned to replace or expand use of the UPC-A symbol.

One concern for a reader that is capable of reading both UPC-A andDatabar-limited symbols is that a complete Databar-limited symbol can befound in a UPC-A symbol, and this may result in a symbol misdecode ormisread. The Databar-limited symbol does not require a clear marginaround the Databar-limited symbol. Hence, a fragment or portion of theUPC-A symbol could contain a completely valid, element-by-element,Databar-limited symbol and, hence, the UPC-A fragment could be mistakenfor a Databar-limited symbol. Analysis indicates that about 89,000 validDatabar-limited symbols could be embedded in a UPC-A symbol. It is alsopossible that a complete Databar-limited symbol can be found in othersymbologies. However, a misdecode from the UPC-A symbol is considered ofmost concern since these two symbologies are expected to coexist in thesame application.

This type of symbol misdecode is more likely to occur if Databar-limiteddecoding is attempted before UPC-A decoding. Yet, even when UPC-Adecoding is designed to be attempted first, this symbol misdecode couldoccur when the UPC-A decoding is disabled and the Databar-limiteddecoding is enabled. This symbol misdecode could also occur when, forexample, a tilted scan line overlies the symbol at an angle inclinedrelative to the horizontal scan direction, rather than entirely alongthe horizontal scan direction, or when the scan line is too short. Inthe case of a handheld reader, a short line could occur if an operatorincorrectly aims the reader at the symbol. In the case of a readerhaving an omnidirectional scan pattern, several tilted short linesalways overlie the symbol at an inclined angle. In the case of animaging reader, a short or a tilted line could occur if the imagerincorrectly recognizes the margin or bounding box surrounding thesymbol. Accordingly, there is a need for an arrangement for, and amethod of, minimizing, and preferably preventing, such symbol misdecodesin such readers.

SUMMARY OF THE INVENTION

One feature of this invention resides, briefly stated, in an arrangementfor, and a method of, minimizing misdecodes of GS1 DataBar Limited(Databar-limited) symbols in a reader for electro-optically readingsymbols of different symbologies. A data capture assembly is operativefor capturing light from a target symbol, and for generating anelectrical signal indicative of the captured light. A programmedmicroprocessor or controller is operative for processing and decodingthe electrical signal, and for determining whether the decoded signal isindicative of a Databar-limited symbol, and for determining whether thedecoded signal has characteristics indicative of a different symbologyother than the Databar-limited symbol, such as a Universal Product Code(UPC) Version A (UPC-A) symbol, to indicate whether a misdecode of theDatabar-limited symbol has occurred.

In one embodiment, the reader is a moving laser beam reader, whichincludes a laser for emitting a laser beam, a scanner for sweeping thelaser beam in a scan line across the target symbol for reflection andscattering therefrom, and a detector for detecting the captured lightfrom the target symbol. In another embodiment, the reader is an imagingreader, which advantageously includes an illuminator for illuminatingthe target symbol, and a solid-state imager, such as a charge coupleddevice (CCD) or a complementary metal oxide semiconductor (CMOS) device,for detecting the return light from the target symbol.

In accordance with this invention, the controller is operative fordetermining whether the decoded signal has characteristics indicative ofa UPC-A symbol to indicate that a misdecode of the Databar-limitedsymbol has occurred. The controller is operative for checking whether afinder pattern of bars and spaces from the Databar-limited symbolmatches a center guard pattern of bars and spaces from a valid UPC-Asymbol and/or for checking whether a finder pattern from theDatabar-limited symbol is one of a set of known finder patternscompatible with a valid UPC-A symbol and/or for checking whethercontextual information from the Databar-limited symbol is available. Thecontroller is also operative for determining whether the decoded signalis indicative of a UPC-A symbol.

The method of minimizing misdecodes of Databar-limited symbols in areader for electro-optically reading symbols of different symbologies,is performed by capturing light from a target symbol, generating anelectrical signal indicative of the captured light, processing anddecoding the electrical signal, determining whether the decoded signalis indicative of a Databar-limited symbol, and determining whether thedecoded signal has characteristics indicative of a different symbologyother than the Databar-limited symbol to indicate whether a misdecode ofthe Databar-limited symbol has occurred.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a handheld moving laser beam reader forelectro-optically reading symbols in accordance with the presentinvention;

FIG. 2 is a schematic diagram of a handheld imaging reader forelectro-optically reading symbols in accordance with the presentinvention;

FIG. 3 is a view of a UPC-A symbol depicting some of its structure;

FIG. 4 is a view of a Databar-limited symbol depicting some of itsstructure;

FIG. 5 is a view of the UPC-A symbol of FIG. 3, wherein the arrowdepicts a fragment which contains a valid Databar-limited symbol of thetype shown in FIG. 4; and

FIG. 6 is a flow chart of steps performed in accordance with the methodof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 depicts a moving laser beam reader 40 for electro-opticallyreading target symbols of different symbologies that may use, andbenefit from, the present invention. The beam reader 40 includes ascanner 62 in a handheld housing 42 having a handle 44 on which atrigger 10 for initiating reading is mounted. The scanner 62 isoperative for scanning an outgoing laser beam from a laser 64 and/or afield of view of a light detector or photodiode 66 in a scan pattern,typically comprised of one or more scan lines, multiple times persecond, for example, forty times per second, through a window 46 acrossthe symbol for reflection or scattering therefrom as return lightdetected by the photodiode 66 during reading. The beam reader 40 alsoincludes a focusing lens assembly or optics 61 for optically modifyingthe outgoing laser beam to have a large depth of field, and a digitizer68 for converting an electrical analog signal generated by the detector66 from the return light into a digital signal for subsequent decodingby a microprocessor or controller 70 into data indicative of the symbolbeing read.

FIG. 2 depicts an imaging reader 50 for imaging target symbols ofdifferent symbologies to be electro-optically read, as well asnon-symbols, which may use, and benefit from, the present invention. Theimaging reader 50 includes a one- or two-dimensional, solid-state imager30, preferably a CCD or a CMOS array, mounted in the handheld housing 42having the handle 44 on which the trigger 10 for initiating reading ismounted. The imager 30 has an array of image sensors operative, togetherwith an imaging lens assembly 31, for capturing return light reflectedand/or scattered from the target through the window 46 during theimaging to produce an electrical signal indicative of a captured imagefor subsequent decoding by the controller 70 into data indicative of thesymbol being read, or into a picture of the target.

When the reader 50 is operated in low light or dark ambientenvironments, the imaging reader 50 includes an illuminator 32 forilluminating the target during the imaging with illumination lightdirected from an illumination light source through the window 46. Thus,the return light may be derived from the illumination light and/orambient light. The illumination light source comprises one or more lightemitting diodes (LEDs) or a laser. An aiming light generator 34 may alsobe provided for projecting an aiming light pattern or mark on the targetprior to imaging.

In operation of the imaging reader 50, the controller 70 sends a commandsignal to drive the illuminator LEDs/laser 32 for a short time period,say 500 microseconds or less, and energizes the imager 30 during anexposure time period of a frame to collect light from the target duringsaid time period. A typical array needs about 16-33 milliseconds to readthe entire target image and operates at a frame rate of about 30-60frames per second. The array may have on the order of one millionaddressable image sensors.

FIG. 3 depicts a standard Universal Product Code (UPC) Version A (UPC-A)symbol designed to uniquely identify a product and its manufacturer. TheUPC-A symbol is a fixed length, numeric, continuous code and employspatterns of bars and spaces to encode a twelve digit code. The first sixdigits represent the manufacturer of a labeled product; the next fivedigits are a unique product identifier code; and the twelfth digit is acheck character, based on the previous eleven digits of data. The checkdigit has a value mathematically based on the first eleven digitsencoded in the symbol. A weighting scheme is used in its calculation, sothat the check digit also protects against transposition errors if thedigits are manually entered.

The structure of the standard UPC-A symbol is physically arranged intohalves. The first six digits (i.e., the left half) and the second sixdigits (i.e., the right half) are separated by two center guard bars.The two symbol halves are then enclosed by two left guard bars and tworight guard bars. The guard bars are start/stop patterns. Each bar orspace of the UPC-A symbol can have four different widths. The narrowestwidth is termed a “module” and, thus, each bar and each space has awidth which may be one, two, three or four modules wide. A module variesbetween 7.8 mils and 26 mils, with 13 mils being nominal. The first sixdigits are encoded as two bars and two spaces within seven modules andis commonly described by a (7, 2) designation. The last six digits arealso encoded as two bars and two spaces within seven modules and iscommonly described by a (7, 2) designation. Each of the right and leftguard bars comprise a bar, followed by a space, followed by a bar and isthree modules wide. The center guard bars comprise a space, followed bya bar, followed by a space, followed by a bar, followed by a space andis five modules wide.

The bar height of either half of the standard UPC-A symbol is greaterthan the width of the respective halves in order to ensure that at leastone of two orthogonal scan lines will be able to pass completely througheach half of the UPC-A symbol, thereby allowing omnidirectionalscanning. The controller can independently decode the left and the righthalves of the symbol. The right, left and center, guard bars are usuallyprinted with a greater height than the other bars in the symbol.

The European Article Numbering (EAN) symbology is a superset of the UPCsymbology. An EAN Version 13 (EAN-13) symbol contains the same number ofbars as a UPC-A symbol, and includes a country code designation. Theproduct numbering code is the same for EAN-13 and UPC-A symbols toidentify a product worldwide.

FIG. 4 depicts a standard GS1 DataBar Limited (Databar-limited) symbol,which was formerly known as a Reduced Space Symbology (RSS) symbol. TheDatabar-limited symbol encodes fourteen digits and is more than 50%smaller than the UPC-A and EAN-13 symbols and, hence, makes itparticularly useful for identifying small and hard-to-mark products suchas produce and pharmaceutical items. The Databar-limited symbol is alsocomprised of a linear arrangement of bars and spaces (each termed as anelement) of various widths that, when decoded, uniquely identify aproduct and its manufacturer, as well as additional information, such asserial numbers, lot numbers and expiration dates and, thus, provides forgreater product identification, traceability, quality control, and moreflexible coding for coupon applications. The Databar-limited symbol isdesigned to replace or expand use of the UPC-A symbol and/or the EAN-13symbol.

The structure of the standard Databar-limited symbol has a left datacharacter and a right data character, each commonly described with a(26, 7) designation and, therefore, each has 7 bars and 7 spaces, and is26 modules in width. A check character or finder pattern is describedwith an (18, 7) designation and, therefore, has 7 bars and 7 spaces, andis 18 modules in width, and is located between the right and left datacharacters. The Databar-limited symbol also has a left guard comprisedof one space and one bar, and a right guard comprised of one space andone bar. The Databar-limited symbol can encode over four trillionnumbers and is 74 modules wide. Each bar and space can be a minimum of 7modules wide and a maximum of 19 modules wide. A checksum is calculatedby multiplying each character's module width by a weighting factor basedon the data character number and the element's ordinal position.

Both UPC-A (FIG. 3) and Databar-limited (FIG. 4) symbols are decodableand readable by readers of the type depicted in FIG. 1 or FIG. 2. Asdiscussed above, a complete Databar-limited symbol can sometimes befound in a UPC-A symbol or the EAN-13 symbol, and this may result in asymbol misdecode or misread. The Databar-limited symbol does not requirea clear margin around the Databar-limited symbol. Hence, a fragment orportion of the UPC-A symbol could contain a completely valid,element-by-element, Databar-limited symbol and, hence, the UPC-Afragment could be mistaken for a Databar-limited symbol. Analysisindicates that about 89,000 valid Databar-limited symbols could beembedded in a UPC-A symbol in a case when both symbols have a standardpolarity, i.e., the bars are printed in a dark color and the spaces areprinted in a light color. Alternatively, symbols can be printed with aninversed polarity, in which case, the bars are printed in a light colorand the spaces are printed in a dark color, thereby yielding many moresuch cases of mistaken symbols. This symbol misdecode could occur, forexample, as described above, when the real or virtual scan line istilted or too short, or when Databar-limited decoding is tried ahead ofUPC-A decoding or EAN-13 decoding, or when UPC-A decoding or EAN-13decoding is disabled and Databar-limited decoding is enabled.

One type of symbol misdecode is illustrated in FIG. 5, wherein the UPC-Asymbol of FIG. 3 is overlaid by an arrow illustrating a short scan lineover a fragment or portion of the UPC-A symbol. The module widths forthe UPC-A symbol, reading from left-to-right, are set forth, togetherwith the module widths for a valid Databar-limited symbol. A box isdrawn around the module widths for a valid Databar-limited symbol thatare contained within, and are common with, the module widths for theUPC-A symbol. One aspect of this invention is to minimize, andpreferably eliminate, such symbol misdecodes in such readers.

Hence, with the aid of the flow chart of FIG. 6, the programmedmicroprocessor or controller 70 is operative, in block 100, for gettinga scan to obtain the electrical signal derived from a target symbol andgenerated by the digitizer 68 or by the electronic circuitry associatedwith the imager 30 and, in block 102, for decoding that electricalsignal and, in block 103, for determining whether the decode wassuccessful. If the decode was unsuccessful, then the controller 70determines whether a preestablished session time has elapsed in block130. If not, then the controller 70 repeats the functions of blocks 100,102 and 103 until the session time has elapsed. If the session timeelapses without a successful decode, then the session ends at block 132.If the decode was successful, now, in a post-decode check, it must bedetermined whether the decode indicated a Databar-limited symbol, and,if so, whether the target symbol was indeed a Databar-limited symbol, asintended, or a fragment of a UPC-A symbol, as not intended. In otherwords, the controller 70 must distinguish between Databar-limitedsymbols and UPC-A symbols. If it is a UPC-A fragment, then a misdecodecould be declared, and the decode results are discarded. If it is not aUPC-A fragment, then a successful Databar-limited decode could bedeclared, and the Databar-limited decode results are sent to a remotehost for further processing.

The post-decode check is performed by one or more of the followingscreening steps. One initial screening step involves having thecontroller 70 check at block 104 whether the decode is a Databar-limiteddecode. If not, then the decode is from a UPC-A symbol or some othersymbology, and the results are sent to block 126 where post-decodeprocessing is performed, e.g., the results are sent to a remote host. Ifthe decode is a Databar-limited decode, then, as discussed above, itcould also be a UPC-A fragment, in which case, additional screeningsteps are performed.

At block 106, the controller 70 checks whether the decode has been seenbefore in the current reading session. If so, then the controller 70checks whether the Databar-limited decoder has been disabled at block120. If so, then the decode must be from a UPC-A symbol. If not, thenthe decode could still be either a UPC-A fragment or a Databar-limitedsymbol, in which case, the controller increments a counter at block 122and, if the count is determined to be high enough at block 124, i.e.,meets a predetermined count, then the decode must be from aDatabar-limited symbol, and the decode is then sent to block 126 forpost-decode processing. If the predetermined count has not been met,then the decode could still be either a UPC-A fragment or aDatabar-limited symbol, in which case, if the session time has notelapsed, then the controller 70 repeats the functions of blocks 100,102, 103, 104, 106, 120, 122 and 124 until the predetermined count hasbeen met, or until block 104 passes control to block 126 when any of thefurther scans that are processed decodes into a UPC-A symbol or othersymbology.

At block 108, the controller 70 checks whether a finder pattern of barsand spaces from the Databar-limited symbol matches a center guardpattern of bars and spaces from a valid UPC-A symbol. As noted above,the center guard pattern of every UPC-A symbol comprises a space,followed by a bar, followed by a space, followed by a bar, followed by aspace and is five modules wide and can be characterized by a set ofmodule widths (1,1,1,1,1). If this set is found in the module widths ofthe target symbol, then there is a chance that the target symbol is aUPC-A symbol, and there is a possibility that a misdecode might bedeclared immediately, or, more likely, that further tests should beperformed. If this set is not found in the module widths of the targetsymbol at block 108, then the Databar-limited decode results are sent toblock 126 for further processing.

The controller 70 could also check at the same block 108 whether a leftor right guard pattern of bars and spaces from the Databar-limitedsymbol matches a (1,1) sequence from a valid UPC-A symbol. As notedabove, each left or right guard pattern of every UPC-A symbol comprisesa bar, followed by a space, followed by a bar and is three modules wideand can be characterized by a set of module widths (1,1,1). If this setis found in the module widths of the target symbol, then there is achance that the target symbol is a UPC-A symbol, and there is apossibility that a misdecode might be declared immediately, or, morelikely, that further tests should be performed. If this set is not foundin the module widths of the target symbol, then the Databar-limiteddecode results are sent to block 126 for further processing.

The various screening checks at block 108 reduce the number of potentialmisdecodes to a relatively small number, which is termed a “blacklist.”Only Databar-limited symbols containing a few finder patterns out of aset of 88 different combinations can be embedded in a UPC-A symbol.Thus, the elements in the vicinity of a (1,1,1,1) sequence are examinedto establish whether they contain sequences characteristic to thoseblacklisted finder patterns. In some systems, it might be also possibleto store a complete blacklist of possible Databar-limited symbols, whichcan be embedded inside a UPC-A/EAN-13 symbol, and then this storedblacklist is used to evaluate the chance of a misdecode. The controller70 stores this blacklist in memory, and checks whether theDatabar-limited finder pattern, or the complete Databar-limited symbol,is or is not on the blacklist. If it is, then the decode could be eithera UPC-A fragment or a Databar-limited symbol, in which case, thecontroller 70 checks at block 110 whether contextual information fromthe Databar-limited symbol is available to confirm that the targetsymbol is indeed a Databar-limited symbol. If such context is notavailable, then the controller 70 sets the counter to a negative countvalue (−Const1) at block 118, and, if the session time has not elapsed,then the controller 70 repeats the functions of blocks 100, 102, 103,104, 106, 120, 122 and 124 until the predetermined count has been met.

To see if such context is available, the controller 70 checks at block112 whether the context is compatible with a UPC-A symbol. In the caseof an omnidirectional reader, after decoding of the blacklisted targetsymbol, scanning continues, and an attempt is made to create a compositescan, which is composed of several previous scan fragments. If another,longer, or safer decode is obtained from the composite scan, then theinitial decoding is withheld. For example, if there are two scans with arecognizable overlap, they are stitched together, and the controllerdetermines if this composite scan can result in a safe decode. If itdoes not, then the controller continues acquiring new scans until eithera safe decode is obtained, or the composite scan is not extended byadding new scans, or a maximum number of scans has been reached. In thecase of an imaging reader, after decoding of the target symbol, asection of the captured image in the vicinity of the virtual scan lineis analyzed in order to find out whether it is possible to obtainanother decode from an extended or tilted scan line. If another, longer,or safer decode is obtained, then the initial decoding is withheld. Forexample, the controller 70 determines if an initial shortened decode dueto a tilted scan line is improved by another scan line, e.g., oneextending entirely across the center of the target symbol, therebyenabling more context to be obtained. If the improved scan line resultsin finding additional bars of similar width, in an area consistent withbeing part of another symbol, then the Databar-limited decode isrejected and disabled at block 114, even if the scan line does notresult in a decode of another symbology. On the other hand, if theimproved scan line does not find additional bars of similar width in thevicinity of the symbol, and the symbol is not too close to theboundaries of the captured image, then the Databar-limited decode can beconfirmed directly, and sent to the block 126 for further processing.

As an alternative to disabling the Databar-limited decode at block 114,the controller 70 could sets the counter to a higher negative countvalue (−Const2) at block 116, and, if the session time has not elapsed,then the controller 70 repeats the functions of blocks 100, 102, 103,104, 106, 120, 122 and 124 until the predetermined count has been met.

Another screening step involves having the controller 70 enable decodingof UPC-A symbols at block 102 at all times, even if decoding of theUPC-A symbology is disabled, in order to find out whether the decodeddata represent a symbol of the disabled symbology. If this is true, andif additionally a Databar-limited symbol was decoded, then theDatabar-limited decode will be canceled if the data which produced it iscontained in that of the UPC-A symbol.

One type of context that the controller can look for involvesdetermining if extra bars are found in the data next to theDatabar-limited symbol, and, if so, increasing the safety marginrequirement. One type of safety margin is redundancy, as shown in block118. That is, a potentially misdecoded symbol can be required to bedecoded several times, each with the identical result, before asuccessful decode is declared. This delay gives the reader an improvedchance to decode the correct symbol. While the Databar-limited symbologycalls for redundancy checks, the symbology does not call for redundancychecks that are dependent on the symbol content. While this may reducedecode aggressiveness for Databar-limited symbols, only a small subsetof such symbols is affected.

An additional contextual analysis involves determining if any bars orspaces are wider than 4 times the unit module width, and/or if every twobars and two spaces add up to a sum of 7 modules. The structuralcharacteristics are indicative of a UPC-A symbol.

It will be understood that each of the elements described above, or twoor more together, also may find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied inelectro-optical readers, it is not intended to be limited to the detailsshown, since various modifications and structural changes may be madewithout departing in any way from the spirit of the present invention.For example, the misdecode described above for UPC-A symbols is equallyapplicable to EAN-13 symbols.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

1. An arrangement for minimizing misdecodes of GS1 DataBar Limited(Databar-limited) symbols in a reader for electro-optically readingsymbols of different symbologies, comprising: a data capture assemblyfor capturing light from a target symbol, and for generating anelectrical signal indicative of the captured light; and a controller forprocessing and decoding the electrical signal, and for determiningwhether the decoded signal is indicative of a Databar-limited symbol,and for determining whether the decoded signal has characteristicsindicative of a different symbology other than the Databar-limitedsymbol to indicate whether a misdecode of the Databar-limited symbol hasoccurred.
 2. The arrangement of claim 1, wherein the data captureassembly includes a laser for emitting a laser beam, a scanner forsweeping the laser beam in a scan line across the target symbol forreflection and scattering therefrom, and a detector for detecting thecaptured light from the target symbol.
 3. The arrangement of claim 1,wherein the data capture assembly includes a solid-state imager havingan array of sensors for detecting the captured light in a virtual scanline from the target symbol.
 4. The arrangement of claim 1, wherein thecontroller is operative for determining whether the decoded signal hascharacteristics indicative of a Universal Product Code (UPC) Version A(UPC-A) symbol to indicate that a misdecode of the Databar-limitedsymbol has occurred.
 5. The arrangement of claim 4, wherein thecontroller is operative for checking whether a finder pattern of barsand spaces from the Databar-limited symbol matches a part of a patternof bars and spaces from a valid UPC-A symbol.
 6. The arrangement ofclaim 4, wherein the controller is operative for checking whether afinder pattern of bars and spaces from the Databar-limited symbolmatches one of a set of patterns of bars and spaces known to becompatible with valid UPC-A symbols.
 7. The arrangement of claim 4,wherein the controller is operative for checking whether contextualinformation from the Databar-limited symbol is available.
 8. Thearrangement of claim 7, wherein the controller is operative for delayingthe decoding when one of the following conditions is met: the contextualinformation is unavailable; the contextual information is incompatiblewith another symbology; decode redundancy criteria is fulfilled; and thecontextual information is found to be incompatible with the symbology.9. The arrangement of claim 4, wherein the controller is operative foralso determining whether the decoded signal is indicative of a UPC-Asymbol.
 10. The arrangement of claim 9, wherein the controller isoperative for combining a plurality of decodes to obtain a compositedecoded signal indicative of the UPC-A symbol.
 11. A method ofminimizing misdecodes of GS1 DataBar Limited (Databar-limited) symbolsin a reader for electro-optically reading symbols of differentsymbologies, comprising the steps of: capturing light from a targetsymbol, and generating an electrical signal indicative of the capturedlight; and processing and decoding the electrical signal, anddetermining whether the decoded signal is indicative of aDatabar-limited symbol, and determining whether the decoded signal hascharacteristics indicative of a different symbology other than theDatabar-limited symbol to indicate whether a misdecode of theDatabar-limited symbol has occurred.
 12. The method of claim 11, whereinthe capturing step is performed by emitting a laser beam, sweeping thelaser beam in a scan line across the target symbol for reflection andscattering therefrom, and detecting the captured light from the targetsymbol.
 13. The method of claim 11, wherein the capturing step isperformed by exposing an array of sensors of a solid-state imager todetect the captured light in a virtual scan line from the target symbol.14. The method of claim 11, and determining whether the decoded signalhas characteristics indicative of a Universal Product Code (UPC) VersionA (UPC-A) symbol to indicate that a misdecode of the Databar-limitedsymbol has occurred.
 15. The method of claim 14, and checking whether afinder pattern of bars and spaces from the Databar-limited symbolmatches a part of a pattern of bars and spaces from a valid UPC-Asymbol.
 16. The method of claim 14, and checking whether a finderpattern of bars and spaces from the Databar-limited symbol matches oneof a set of patterns of bars and spaces known to be compatible withvalid UPC-A symbols.
 17. The method of claim 14, and checking whethercontextual information from the Databar-limited symbol is available. 18.The method of claim 17, and delaying the decoding when one of thefollowing conditions is met: the contextual information is unavailable;the contextual information is incompatible with another symbology;decode redundancy criteria is fulfilled; and the contextual informationis found to be incompatible with the symbology.
 19. The method of claim14, and determining whether the decoded signal is indicative of a UPC-Asymbol.
 20. The method of claim 19, and combining a plurality of decodesto obtain a composite decoded signal indicative of the UPC-A symbol.